Program-controlled communication systems have a central controller and subscriber line modules connected thereto with which are realized communication terminals for a connection of communication terminal equipment. For example, a subscriber line module makes available 24 communication terminals to which at least 24 communication terminal equipment are connectable. A signaling channel (known as D-channel in the technical field) having, for example, a standardized transmission capacity of 16 kBit/s is conducted via each of these communication terminals. Signaling messages are sent both to the communication terminal equipment as well as to the communication system via the signaling channel. A substantially higher flow of signaling messages from the communication system to the communication terminal equipment units occurs due to the switching-oriented settings of the user surface of the communication terminal equipment units (particularly given stimulus communication terminal equipment) by the communication system. Particularly given specific uses of the communication terminal equipment, this can lead to an elevated flow of signaling messages from the communication terminal equipment and, thus, to an overload of the subscriber line modules.
Further, the subscriber line modules each respectively have a microprocessor system with which the processing requests communicated from the processes implemented in the subscriber line modules are processed. The processes are thereby organized as autonomous tasks that have various priority levels with respect to the message processing. The resource processing capacity of the microprocessor system is provided within a subscriber line module for message processing in the inter-process communication and for resource administration of the further resources on the subscriber line module. An overload of the microprocessor system is caused both by substantial message flow in the direction of the communication terminal equipment units as well as by the messages to be communicated to the central controller.
A known method for identifying the overload of a subscriber line module is to utilize the plurality of memory elements that are still free in a memory element pool administered by the operating system. The memory elements are temporarily allocated to the respective processes or, respectively, tasks for the intermediate storage of information, i.e. the respective process can store its data or, respectively, information on the memory elements allocated to it.
An exclusive monitoring of the memory element pool for a judgement of an overload is disadvantageous since the overload condition is recognized too late and, thus, fast-acting counter measures cannot be initiated. The subscriber line module is switched into a disturbed condition after the transgression of an overload threshold and this can only be canceled by a restart, i.e. a reset of the subscriber line module.